Conventionally, a method that increases the vertical resolution of pictures by increasing the number of scan lines in the vertical direction in each field is known as a method for improving the picture quality of video signals that are provided based on methods such as NTSC and PAL. In a line doubling device that performs such processing, three input signals are inputted and a video signal with double the number of scan lines is generated.
The scan line doubling process that generates a field in which the number of scan lines has been doubled from a plurality of video signals in this way is composed so as to change the combination of video signals supplied to the line doubling device in accordance with the video source of the input video signal. In a case where the video source of the input video signal is a video source that supplies a different picture in each field, such as a normal broadcast signal or an output signal from a video camera according to NTSC or the like, the video signals for three consecutive fields are supplied to the line doubling device using a delay means and the correlation between fields and the correlation within fields are used to generate fields with double the number of scan lines.
FIG. 1 shows pictures of fields that are consecutively outputted from this kind of video source. In FIG. 1, the fields specified by symbols such as a, c, e to which a dash has not been appended indicate the odd-numbered fields in a frame, while the fields specified by symbols such as b′, d′ to which a dash has been appended indicate the even-numbered fields in the frame. It should be noted that dashes appended to symbols specifying fields also have the same meaning in the following explanation. As one example, in a case where an interlaced (525i) picture with 525 scan lines per frame is converted into a progressive scan (525p) picture with 525 scan lines per frame, a progressive scan picture with 525 lines per field is obtained by performing predetermined signal processing on pictures, for example the picture of field a (262.5 scan lines), the picture of field b′ (262.5 scan lines), and the picture of field c (262.5 scan lines), that are provided as consecutive interlaced pictures.
Furthermore, in the case where an NTSC video signal that has been generated based on a movie film is the video source (hereinafter, this is referred to as a “film source”), since an NTSC video signal has 30 frames per second (60 fields per second) as opposed to a movie film that has 24 frames per second, a field conversion process called a 3-2 pull-down is performed to generate an NTSC video signal based on the movie film. FIG. 2 shows a field conversion operation based on a 3-2 pull-down. In FIG. 2, FIG. 2A shows the pictures of two consecutive frames and FIG. 2B shows the pictures of five consecutive fields. In this way, three consecutive fields a, a′, a are generated from the first frame and two consecutive fields b′, b are generated from the second frame.
When a film source is the video source, in view of the special characteristics of the video signal described above, three video signals, made up of a video signal of the odd-numbered field, a video signal of the even-numbered field, and a video signal of the odd-numbered field generated from the same frame, or alternatively a video signal of the even-numbered field, a video signal of the odd-numbered field, and a video signal of the even-numbered field generated from the same frame, are supplied in synchronization to the line doubling device as described later. Accordingly, since the combination of video signals supplied to the line doubling device differs between the case when a film source is the video source and the case when a film source is not the video source, if a film source is used as the video source and video signals of three consecutive fields are inputted into the line doubling device, problems such as a lowering of resolution occur and it is not possible to perform the line doubling process effectively.
It should be noted that when a PAL video signal is generated based on a movie film, in the same way a field conversion process called a “2-2 pull-down” is performed. While a movie film has 24 frames per second, a PAL video signal has 50 fields per second, so that two consecutive fields are generated from the video of each frame.
Accordingly, in a video signal processing apparatus that includes a line doubling device, the video source of an input video signal is determined, and different combinations of video signals are supplied to the line doubling device in a case where the video source is a film source and in a case where the video source is not a film source, so that high resolution fields in which the number of scan lines has been doubled are generated, thereby increasing the resolution.
However, a video signal processing apparatus that includes a conventional line doubling device is constructed as described above, and in a case where the judgment performed for the video source of the input video signal has low accuracy or when a suitable scanning method is not used for the output video signal in accordance with the determined type of video source, there has been the problem that it has not been possible to display a favorable picture on a television receiver based on the output video signal obtained from the line doubling device.